An invasive species of mussels was found at the site of a former fish farm in the Garden State.

Chinese pond mussels are wreaking havoc in Eastern Europe, but had never been seen in the United States before they showed up in New Jersey.

"Nobody knew what they were," says Emile DeVito, of the NJ Conservation Foundation. "We thought they were a native mussel--only they seemed way too big. When biologists at the University of North Carolina identified them, it was like a giant biological burglar alarm going off."

Experts says that the Chinese pond mussel caused damage in other ecosystems. Elizabeth Ciuzio, of Freiday US Fish and Wildlife Service, says the shells are so big they can change the river surface.

State and federal agencies along with the conservation foundation spent all summer digging the mussels from the nine ponds they were found in. They then treated the water with a copper-based additive that kills them.

Since September, the mussels appear to be gone and have not spread.

"Imagine when I retire in 20 or so years and the Chinese pond mussel is everywhere--I have to live with I knew there was one here and we had the resources to assist," Ciuzio said. "So it became very important to us. Testing continues to make sure."

The former fish farm had held carp that were raised for Asian food markets in New York City. The pond mussel's larvae is believed to have arrived in the gills of fish the farmer had imported from Asia.